Preparation of photographic sound records



Feb. 9, 1932. D. T. BENNETT 1,844,880

PREPARATION OF PHOTOGRAPHIC SOUND RECORDS Filed Jan. 15, 1951 PatentedFeb. 9, 1932 noucms TEMPLE 13mm, or wnvcrmonn HILL, ENG-LAND PREPARATIONOF PHOTOGRAPHIG SOUND RECORDS Application filed-January 13, 1931, SerialNo.

This invention relates to the preparation of so-called photographicsound records, such as those of so-called talking films, and inparticular to the means which are employed for producing thevaryinglight which is employed. v

The invention has for an object to rovide an improved method of andmeans or producing a varying light or glow emission corresponding with avarying electric current, such as the so-called speech current from amicrophone.

According to the invention, a method of producing a varying light orglow emission corresponding with a varying electric current consists inpassing a varying electric current through an electrode, of which a partat least is comprised by a resistance element, of

- an electric glow discharge device, such as a neon lamp.

The flow of varying electric current through a resistance electrode of aglow discharge device may serve to modify the potential difierencebetween it and another elec- 5 trodeofthe device, and hence the glowemitted by the latter. Alternatively, the flow of varying electriccurrent through a single, resistance, electrode of a glow dischargedevice may serve to modify the potential difierence between partsthereof, and thus to modify the glow emitted.

" In cases where the flow of varying current through aresistanceelectrode serves to modify the potential difference between it and asecond electrode, it is desirable that the resistance electrode shouldbe connected at'one end, or at a given point in the length thereof,

through a source of electro-motive force, with said second electrode. Inall cases, however, it is desirable that asource of constantelectromotive force should be connected in series or in parallel withthe resistance electrode, so that when no varying current flows throughthe latter, there will be a fall in potential along the resistanceelectrode which will be modified as soon as varying current flowstherethrough.

The invention is illustrated by the accompanying drawings, which arecircuit dlagrams, of which 508,511, and in Great Britain January 9,1930.

showing a dischargedevice having a single electrode;

Figure 3 is a diagram of the type of sound record obtained by the use ofeither of these circuit arrangements;

Figures 4 and 5 show alternative arrangements employing two electrodesin a single on discharge device, respectively, and

Figure 6 is the type of sound record to be obtained by the use of eitherof these arrange ments.

Referring first to Figure 1 of. the drawas merit or coiled resistancewire extending 7 alongside the first from end to end. One end 14 of theresistance electrode is connected through a source of constantelectro-motive force 15, such asa high tension battery, with theequipotential electrode 12, whilst to that pole 16 of thisinterelectrode source 15, which is connected with the end 14 of theresistance electrode 13, is connected in this particular case a (like)pole 17 of a second source or battery 18, the other pole so 19 of whichis connected through a source of varying electric current; such as thesecondary winding 20 of an output transformer of an audio-frequencthermionic valve amplifier (not shown) with the other end 22 of the re-86 sistance electrode 13. In cases where it is undesirable that thesteady flow of current through the resistance electrode 13 should passalso through the source of speech current 20, (e. g. to avoid 90saturation of an iron core), the source 18 of electro-motive force(hereinafter referred to as the biassing source) may be connect- ,ed inparallel with the resistance electrode 13, whilst the source of varyingelectric current 20 is connected in shunt wlth, or across, this parallelcircuit through the medium of one or more electro-static condensers.Such an arrangement is to all intents and purposes virtually the sameelectrically as that shown in Figure 1, and is therefore notillustrated.

In either case, however, it will be observed, firstly, that thepotential difierence between the end 14 (hereinafter referred to as theconstant potential end) of the resistance electrode 13 and theequipotential electrode 12 will remain always constant at a value equalto the potential of the interelectrode source 15, and, secondly, thatwhen no vary ing current flows, the potential between the other end 22of the resistance electrode 13 (hereinafter termed the varying potentialend) and the equipotential electrode 12 will be less (more if the source18 be reversed) than the potential of the interelectrode source 15 by.an amount depending upon the steady current flowing through theresistance electrode 13 from the biassing source 18; the

interelectrode potential increasing alongthe length thereof, i. e. fromthe maximum at the constant potential end 14 of the resistanceelectrode. The potential of the bias'sing source 18 should not be lessthan the maximum peak potential of the varying current from the source20. Thus, when the varying current flows, corresponding potentialvariations will alternately assist and oppose the potential of thebiassing source 18, so thatthe interelectrode potential difference atthe varying potential end 22 of the resistance electrode 13 willalternately decrease and increase with the varying current. As a result,the

interelectrode glow, which, when no varying current flows, extends, forexample, half way along the interelectrode space, as indicated at g,from the constant potential end 14, Wlll vary in length from said endbetween two extremes; at one, the shorter, of which the varying currentpeak potential assists the biassing source 18, and at the other, thelonger, of which said peak potential opposes the biassing source; thevariations in the length of the glow being exactly in accordance withthe Variations in the Varying cur-\ rent, in amplitude and periodicityand being produced by variations in the position of that point in thelength of the electrodes at which the potential between said electrodesis at that critical value which is just suflicient to cause a glowemission.

In the case of Figure 2 of the drawings, a glow discharge device 23 hasa single electrode only comprised by two limbs 24 and 25, each in theform of a resistance element. A source 26 of varying electric current isconnected in series with a biassing source of constant electro-motiveforce 27 across the ends 28. 29 of the electrode 24, 25 and thepotential thereof is so chosen that normally the glow will extend fromthe free ends 28, 29 of the limbs 24 and 25 to a point intermediately oftheir length, as, in this case also, indicated at g.

From the above it will be apparent that as the varying electric currentfrom the source 26 alternately assists and opposes the biassing source27, so will the length of the glow between the two electrode limbs 24and 25 increase and decrease in length from the free ends 28, 29 of saidlimbs.

With this arrangement of Figures 1 and 2 of the drawings, it is possibleto obtain a sound record of the type shown in Figure 3, the glow beingprojected upon a moving strip of sensitized material in a known orconvenient manner. So long as no varying current flows, a given constantwidth, say one half of the strip from side to side, may be affected orexposed, as shown at 30, Figure 3. Upon the flow of varying current, theboundary of the affected or exposed part of the strip will change from astraight line to a line, the distance of which from the edge of thestrip will vary in accordance with the varying electric current, asshown a; 3

A linear or area record obtained in this manner is much more accurate(i. e. free from distortion) than those obtained by the use ofoscillograph devices, owing to the complete absence of moving parts andthe consequent inertia lag.

As shown in Figure 4, it is possible, by the use of a resistanceelectrode 32 having a constant potential point intermediately of itslength, preferably midway between its ends, as shown at 33, instead ofat one end, that the interelectrode glow of a two-electrode dis chargedevice 34.- may be caused to expand and contract at both ends lengthwiseof the electrodes '32 and 135 from the given or normal length, indicatedin this figure also by 9, so that there may be obtained a record (seeFigure 6) in the form of an affected or exposed band extending centrallylengthwise of a strip of sensitized material, both boundaries of whichband, and thus the overall width, will be varied from the normal, shownat 36, in accordance with the varying current to be recorded, as' shownat 37.

In such a case two biassing sources of electro-motive force, and twoindependent feeds from a source of varying current to the sections ofthe resistance electrode 32 at either side, respectively, of theconstant potential point 33 of the latter may be employed, but, as shownin Figure 4, an interelectrode source 38 is connected between theequipotential electrode 35 and the constant potential point 33 of theresistance electrode 32; a biassing source 39 and a source of varyingcurrent 40 being connected in series between said constant potentialpoint 33 and the free ends, respectively, of the resistance electrode32.

In order to obtain a glow emission capable of expanding, as in the caseof Figure 4, at both ends, a single electrode glow discharge device maybe arranged, as shown in Figure 5 of the drawings, for example, toobtain a record such as shown in Figure 6. In this case a glow dischargedevice 41 is provided with a single electrode having two pairs of limbs42, 43 and. 44, 45, respectively, the limbs of each pair being connectedin series, whilst i the limb 45 is connected with the limb 43 of thefirst pair. The junction of the limbs 43 and 45 is connected through abiassing source 46 and a source of varying current 47 with the junctionof the limbs 42 and 44 of the electrode. It will be observed that inthis case the glow emitted will vary in length from the normal,indicated by g, in accordance with the/varying electric current from thesource 47, which will alternately assist and oppose the biassing source46.

It is well-known that linear or area records of the kindv illustrated inFigures 3 and 6 are much less subject to inaccuracies brought bydevelopments and printing processes, to which photographic sound recordsmust inevitably be subjected, than are density records in which theopacity or transparency across the full width of a record strip variesin accordance with the recorded varying cur.- rent.

It will be observed by those skilled in the art'that by the use of avarying glow in an electric glow discharge device according to theresent invention, it would be possible to o tain a combined linear orarea and;

density record, i. e. a record in "which the opacity or transparency ofthe affected or exposed band of a sensitized stripwhich vanes wlthitswidth, which in turn varies in accordance with the recorded current.Such a combined type of record could be obtained creases in length fromthe constant potential point, or end of the resistance electrode, so theintensity of the glow at that point or end will increase or decrease.Here it should be noted that in all cases, see Figure 2, there will be aconstant potential difference between the free ends '28 and 29 of thesingle electrode and that in Figure 5 this constant potential willobtain between the junction of the limbs 42, 44 and of the limbs 43, 45.

In Figures 4 and 5. the arrangement is such that the glow expands andcontracts from the centre of the tube, but it will be apparent thatanalogous arrangements could be used where the glow extends from eachend of the tube towards the. centre.

It will also be observed that where an equipotential electrode isemployed, this may intensity of the glow.

Insome cases itmay be possible, with a view to rendering the variationsin glow in length or area more directly proportional to the varyingelectric current which produces them, to employ other than straightelectrodes and/or to mount the electrodes at an angle to one another.Again, it may in some cases be desirable that the resistance of theresistance electrode should not be constant per unit length.

Finally, it will be observed that where one or two electrodes areemployed, either orboth may take various forms for example, a resistanceelectrode could be of substantially spiral formation and used inconjunction with an equipotential electrode in the form of a circularplate mounted alongside it.

Various gases and combinations of gases may be employed in the glowdischar e device, and it has been found that, alt ou h the varying glowemission according to t e invention is intended particularly for use inthe production of photographic sound records, it could also be usedinter alz'a in connection with a suitable viewing mechanism as anoscillograph for communication urposes, or even in electric signs, inwhich t e electrode or electrodes could be in the form of symand oneequipotential electrode. Moreover,

inasmuch as rays emitted by an electric glow discharge device are notnecessarily within the range of a visible spectrum, the varying glowaccording to the present inventionneed not necessarily be a visible, orwholly visible one.

What I claim is 1. A method of producing a varying light or glowemission corresponding with a varying electric current, which consistsin passlng the varying electric current through an electrode, of which apart at least is comprised by a resistance element, of an electric glowdischarge device, such-as aneon lamp.

2. A method of producin a varying light or glow emission correspon ingwith a varying electric current, as claimed in claim 1, wherein the flowof varying electric current through a single. resistance, electrode ofthe discharge device serves to modify the po- 3.'A method of producing avarying light or glow emission corresponding with a varying electriccurrent, as claimed in claim 1, wherein a resistance electrode isconnected at one end or at a given point in the length thereof through asource of electro-motive force with another electrode of the device. j

4. A method of producing a varying light or glow emission correspondingwith a varying electric current, as claimed in claim 1,

x i \l wherein a resistance element is connected at e a pointintermediately of its length with one pole of a source of varyingelectric current, the other pole of which is connected with the 5 endsof said electrode.

In testimony whereof I have hereunto signed my name.

DOUGLAS TELIPLE BENNETT.

